Interspecific somatic cell hybrids retaining the 21st and the X human chromosomes will be analyzed by 2-D gel electrophoresis in order to identify those gene products encoded by these chromosomes. Hybrids retaining and lacking the human 21 and X chromosomes will be generated. Human gene products will be distinguished from mouse gene products by employing dual-label techniques and computerized analysis. The proteins identified as mapping to chromosome 21 will be tested for gene dosage effects in monosomy 21 and trisomy 21 cells using quantitative computerized analysis. Expressed levels of 21 and X specific proteins will be measured during in vitro fibroblast aging and following addition of hydrocortisone. X chromosomal proteins which have escaped x-inactivation will be searched for using quantitative 2-D analysis of XOXY, XX, and XXXXX cell lines. Subcellular fractionation will be employed in a variety of ways in order to expand the number of identifiable gene products. Activation of tissue specific gene product expression from chromosomes 21 and X will be examined. Suppression of gene expression and reactivation following experimental viral infection will be investigated. Characterization of identified proteins will include antigenic methods, biochemical properties, tissue distribution, tryptic peptides, amino acid composition, and turnover times. Abnormalities of gene dosage expression are the likely causes which lead to the aneuploid phenotypes, some of which show premature aging. The proposed investigation has the potential to define up to 1000 or more human gene products of the 21 and X-chromosomes. Some of these likely relate to the aging effects of aneuploidy, such as occurs in Down's syndrome.